Earlier this year, construction workers discovered what is now the world's oldest known bra. It dates to the 15th century and was found with a bunch of other clothing, stuffed between the floors of an Austrian castle. Most likely, it was being used for insulation, the same way we might stuff a wall with fiberglass batting today. (Via Christopher Mims)

Right now, I'm reading The Conundrum by David Owen. It's a really interesting book about some of the unintended consequences of the way we approach sustainability and environmentalism.

I'm going to post a full review soon, once I get all the way through it, but so far Owen is making a couple of key points: One that I agree with, and one I think he's oversimplifying a bit. I agree with this: You can't shop your way out of climate change. The tendency to turn environmentalism into a set of luxury lifestyle choices is a huge problem—doing nothing to solve our energy issues and perpetuating an idea that sustainability is "for" some people and not for others.

Owen also talks a lot about the rebound effect (or, as it's sometimes called, Jevons Paradox)—a very real problem that affects our ability to reduce emissions caused by energy use. Basically, it works like this: when you reduce energy use through energy efficiency, you get the same amount of work for less energy investment. That's good. But saving energy also saves money. That saved money often ends up spent in ways that consume energy. In the end, some measure of the energy you thought you saved through energy efficiency ends up not actually being saved. It just got consumed in another place. The result is good for the economy, but maybe not so good for the climate, depending on how the energy in question was produced.

So far, Owen seems to be taking the position that the rebound effect will always negate all the environmental benefits of energy efficiency programs. From the research I did while working on Before the Lights Go Out
, my upcoming book on the future of energy, that's probably not correct. Like I say, I'm not done with Owen's book yet, so I'll let you know what he has to say on this issue in more detail later. But I wanted to bring it up now as an excuse to link to an in-depth FAQ on the rebound effect that I co-authored with Karen Turner, an economist who is one of the few people actually studying how the rebound effect works in the real world.

A lot of the statements made about the rebound effect are based on "common sense" logic and computer models that don't necessarily portray consumer behavior in a realistic way. People like Turner, who do empirical research on the subject, present a more nuanced view.

This FAQ—which is basically a transcript of my first interview with Turner, done 2010—will help you understand why rebound happens, why it's not strictly a bad thing, and what (if anything) we can do to make energy efficiency a useful tool in the fight against climate change.